In low-dose rate (LDR) brachytherapy and high-dose rate (HDR) brachytherapy an introduction element like a catheter or a needle for introducing a radiation source is inserted into a person by a physician under ultrasound imaging guidance, in order to treat an inner region of the person with radiation emitted by the radiation source. During the insertion process the physician has to manually control the position and image plane of an ultrasound transducer, which leads to inaccuracies in imaging such that the tip of the introduction element is not always visualized accurately relative to a target region within the person, where the tip should be finally located. The physician performs therefore often an iterative process comprising multiple attempts to guide the tip of the introduction element to the target region. This leads to a temporally long and not very accurate insertion process.